Customarily catalytic converters are employed for accelerating or improving chemical reactions. Catalytic converters are employed in particular in industrial combustion systems for cleaning flows of fluids of substances which are being carried along. The catalytic converters have a surface with active centers at which the substances carried along in the fluid flow are either adsorbed and/or absorbed. The adsorbed and/or absorbed substances are subjected to a reaction with other substances contained in the fluid or with reagents specifically added for this purpose to the fluid, and the reaction products are released and are carried along in the fluid flow.
In connection with the use of catalytic converters in combustion systems, flue gas being generated in the course of the combustion is passed by the highly porous ceramic catalytic converters along the surface of the catalytic converters for converting undesired substances into less critical or harmless substances. Catalytic converters are used in particular for converting nitrous oxides present in the flue gas. In so-called selective catalytic reduction methods (SCR), NOx (nitrous oxides) is reacted with NH3 (ammonia), which is specifically added to the flue gas as a reducing reagent, to form water (H2O) and nitrogen (N2).
The surface of the catalytic converters and the catalytically active centers located thereon must be accessible to the fluid flow (e.g. flue gas) so that the catalytic converter can perform its catalytic effect on the harmful constituents of the fluid. In particular, the access paths to the surface must be free, and the surface free of blocking and/or blinding layers and catalytic poisons, which over time collect there in the course of operation. Otherwise the catalytic converters lose a portion of their catalytic activity because of chemical reactions of catalytic poisons with constituents of the flue gas rendering the catalytically active sites on the catalyst's surface catalytically inactive, plugged and/or clogged pores in the catalytic converter, and blocking and/or blinding layers, as well as plugged and/or clogged channels.
Methods for treating SCR catalytic converters with cleaning agents are known from PCT Patent Publication WO 00/001483 or PCT Patent Publication WO 04/073835. However, for this purpose it is necessary to disassemble the catalytic converters from their assembled, operationally ready state, and to transport, treat, again transport and reassemble them.
U.S. Pat. No. 6,631,727 describes a method wherein catalytic converters (blocks of catalytic converters) can be treated in the installed state in that a cleaning agent is conducted from above through the conduits and collected at the other side of the channels. On the one hand, not all the dirt is loosened during this one-sided flushing, on the other hand the method is elaborate/cumbersome, since it is necessary to provide work areas on both sides of the blocks of catalytic converters, where material and equipment for introducing and/or collecting the fluid must be made available.
It is the object of the present invention to provide a method which permits a simple, efficient and cost-effective cleaning and/or regeneration of catalytic converters.